(1) Field of the Invention
This invention relates to light source, particularly to the use of multicolor light emitting diode (LED) light source to produce a white light.
(2) Brief Description of Related Art
FIG. 1A shows a prior art to produce a colorless white light. The light source uses three color LEDs to produce a white light. A red color LED R, a green color LED G, and a blue color LED B are mounted on a substrate 10, The three LEDs are then covered with a glue for protection.
FIG. 1B shows the color spectrum of such a light source. The red LED has a light spectrum with wavelength in the 580 nm-680 mm range and a peak at 640 nm. The green LED has a light spectrum with wavelength in the 480 nm-580 nm range and a peak at 530 nm. The blue LED has a light spectrum with wavelength in the 430 nm-530 nm range and a peak at 480 nm. The white light in nature has light spectrum ranging from 400-780 nm wavelength. The artificial white light source using the R, G, B LEDs has peaks at 640 nm, 530 nm and 480 nm wavelengths, but lacks light spectrum below 430 nm wavelength, around 500 nm wavelength, around 580 nm wavelength and above 680 nm wavelength. Therefore, the combination of three color LEDs does not reproduce a true colorless light.
An object of this invention is to produce a colorless light source having the same light spectrum as the white light in nature. Another object of this invention is to produce a white light source with broader light spectrum than using the three color R, G, B LEDs. Still another object of this invention is to lower the cost of reproducing colorless light than the cost of using three color R, G, B LEDs.
These objects are achieved by using only two color LEDs and coving them with color phosphorescent glue. Alternatively, a single color LED is covered with two kinds of colored phosphorescent glues.